Lens.



No. 7I6,035. Patented Dec. l6, I902.

C. A.. H. HABTING.

LENS.

(Application filed Feb. 4, 1901.) (No Model.)

- t airr nr OFFICE.

CARL AUGUSTL HANS HARTING, OF BRUNSWICK, GERMANY, ASSIGNOR TOVOIGTLANDER 8c SOHN AKTIEN GESELLSOHAFT, OF BRUNSXVIGK,

GERMANY.

LENS.

SEECIFISATION forming part of Letters Patent No. 716,035, dated December16, 1902.

Application filed February a, 1901- Serial No. 4:6,008. (N0 model.)

To all whom it may concern.-

Be it known that I, CARL AUGUST HANS HARTING, manager, a subject of theDuke of Brunswick, residing at Brunswick, Duchy of Brunswick, Germany,have invented certain new and useful Improvements in Lenses, of whichthe following is a specification.

This invention has for its object a lens system corrected symmetricallyand also achromatically, spherically, and astigmatically for wideapertures.

If in an objective formed of similar pairs of lenses the kinds of glassare graded in such a way that they also possess, in combination with alarge index of refraction, great color dispersion, it may, as is wellknown, be corrected spherically for any desired size of aperture, butnot astigmatically. If, on the other hand, such an objective be formedof kinds of glass with the larger indices of refraction having a smallercolor dispersion, a considerable improvement results, as is well known,in the position of the astigmatic picture-surfaces, but not suflicientspherical correction for even medium apertures. The present inventionaffords, however, for large apertures a complete spherical correctionboth on and outside the axis, and, further, removes astigmatism andcurvature in the field of vision.

The arrangement is as follows: Between two symmetrically-arrangedsystems of either one or other kind hereinbefore mentioned a thirdsystem is symmetrically arranged relatively to the two outer ones andwhich may consist of one lens. Whether this system is required to beconverging or diverging, the whole system may be spherically corrected.In order, however, to remove the astigmatism and curvature of the fieldof vision left by the outer systemsthat is to say, to correct theobjective into an astigmatic lens-the kinds of glass to be used arechosen in the following manner: The two outer lens systems consist, asalready mentioned, at least of two lenses, crown and flint glass, andthe crownglass must have in both systems either a larger or a smallerindex of refraction than the respective flint-glass. The third system,

inserted between the two, must, however, be so selected that the kindsof glass of which it is composed will correspond in agiven manner to thekinds of glass of the outer systems which stand opposite to its faces,and, in fact, one glass with a large index of refraction and a smallcolor dispersion must face a similar one the index of refraction ofwhich is smaller or approximately as great as that of the other, whileits color dispersion is greater. By this means it is possible, inconsequence of the removal of the faults resulting from sphericalabberration, to obtain first in the center of the picture anextraordinary sharpness, the cause of which is in the reduction orremoval of the intermediate spherical defects. As, however, thespherical aberration of the oblique group of rays is at the same timealmost completely removed and as it is possible to produce an astigmaticleveling over the whole field of vision, which, for instance, amounts toabout fifty degrees for a relative opening of a Let-.5, it follows thatthe optical picture with a sufficient expansion has an extraordinarysharpness even outside the optical axis. As the whole system issymmetrically arranged in itself, the distortion is removed, so that itis practically unnoticeable, so that the picture that is formed isalmost perfectly true. As an example a case which is typical for theobject of the application will be explained.

The accompanying drawing shows the objective.

The outer systems may be formed each of two lenses a and b, of which thetwo lenses a are made of flint-glass and the two lenses 1) ofcrown-glass of higherrefractive index and smaller light dispersion. Thesymmetricallyarranged central lens a must then be made of crown-glass,the index of refraction of which is lower or only equallyas large andits color dispersion largerthan that of the crown-glass of the lensesZ). If the four different radii of curvature of the lenses correspondingto the object sought aft-er are indicated in the drawing by r r r r andthe thicknesses of the lenses by d (Z d d, a calculation yields the following equivalents: 1" equals +41.0, 9' equals +25.76, 0' equals 5S3.8,0'' equals et4=.76, d equals +1.6, d equals +3.6, (1 equals +8.1, d"equals +1.6. The equivalents of the kinds of glass are here assumed tobe the following: For a and c, a equals 1.5638, n

equals 1.5811; for a and b, a equals 1.6080, n" equals 1.6217. The sizeof the aperture, which may be indicated for this objective with a focallength of one hundred, amounts to twenty-five; the diameter of theutilizable picture, eighty. The blind or shutter e is placed directlybehind the central lens.

I declare that what I claim is I A com pound objective lens comprisingtwo groups of lenses, the outer lens of each of the groups constructedof flint-glass and the inner lens of crown-glass, the latter being of ahigher refractory index and smaller color dispersion than the former,and a crown-glass

